Indicator device



June 18, 1957 R. B. KOEHLER 2,796,553

INDICATOR DEVICE Filed Oct. 24, 1955 INDICATING CATHODE KEEP ALIVE UATHODE \24 (100;: AMAX) 55 26 Dc POWER @RT NE SUPPLY susmu. 34 (ISOZOOVOLTS) PULSES 40 38 DC BIAS (IO-iSVOLTS) INVENTOR.

ROBERT B. KOEHLER Qiwf ' AGENT znaasss 'rsurcaron DEVICE -Rbert E. Koehier; Hopewell lunction, N. Y., assignor to International Business Machines Corporati-on, New York,N.Y., a corporation-of New York This invention relates to indicator devices and more particularly to a circuit arrangement including a gaseous discharge tube operable to detect volt-age changes of low magnitude.

An objective of this invention is to improve the versatiiity of devices of this character for which there has long been a need in computer, communication and other electrical arts where sensitivity is of particular importance, as for example in connection with transistor circuits where voltage variations of low order occur.

In accordance with the present invention a gas filled glow transfer discharge tube is provided having a pair of cathodes and a single anode electrode. 'A glow discharge is normally maintained between the anode and one of the cathodes with these electrodes constructed and arranged so that the glow is not externally visible. This first discharge ionizes the gaseous atmosphere in the region between the second cathode andthe anode so that low voltage s'ignalpulses applied to this cathode may initiatea glow discharge thereon. The second cathode is physically positioned where aglow discharge between it and the anode is visible to thereby indicate that such signal pulses are being applied. Means are al'soprovided to periodically extinguish the glowtothe second cathode so th'at'only'the 'continuous'application of signal-pulses or of a steady state voltage level is indicated by the device.

One broad object of the invention, then, is to provide an improved gaseous discharge tube-and circuit arrangement therefor capable of detecting and visuallyindicating the application of low voltage signals.

A further object of the invention is to provide a gaseous discharge indicator tube wherein a glow discharge is maintained to a first electrode in order to lower the breakdown voltage required to initiate a discharge on a second electrode and wherein only the discharge to the second electrode is externally visible.

Another object of the invention is to provide a gaseous discharge tube circuit capable of visually indicating the receipt of a serith of signal pulses of predetermined magnitude.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated of applying that principle.

The single figure illustrates the novel discharge tube structure and circuit arrangement adapted for its use as an indicator for low voltage signals.

Referring now to the drawing, the discharge device comprises an envelope 14) of glass or other transparent or translucent vitreous material containing an ionizable gaseous atmosphere at glow discharge pressures, as for example neon, argon or mixture thereof at a pressure of 20 mm. of mercury. Within the envelope there is supported in conventional manner an anode 12, a cathode 14- and a further cathode 16. The anode 12 is an elongated element preferably fabricated of a refractory material such United States Patent if? Patented June 18, 1957 race as nickel'or molybdenum. The cathodes 14 a-nd'16 are made of similar refractory materials with the cathodei14 preferably formed as a rod-like element and spaced from the anode, and the cathode 16 formed as a U-shaped element positioned axially with respect to the anode and spaced from the cathode14. A cylindrical element 17 is aflixed to theanode '12'and encircles the cathode 14 at its upper end so as to prevent. external light emission when a pled through a lead 24 and a resistor 26 to the negative terminal of the power supply 20, which may be a grounded source as shown. A transformer 30 is also provided, with the terminals of the resistor 26 coupled to the secondary winding 32 thereof throng-ha rectifier-34 that is poled to allow current flow in adirection to increase the voltage ofthe source 20. The primary winding 35 of the transformer 30 may be coupled to an alternating power supply which functions to periodically energize the secondary winding of the transformer. The cathode 16 is coupled through 'alea'd -36 to a source of negative signal pulses or "voltage levels not shown. The other terminal of the sign'al pulse source is connected by a lead 38 to the negative side of a further bias source 43 which is also connected to the grounded terminal of the sourcelt).

In accordance with the particular embodiment illustrated, the above mentioned alternating power supply 'may be a conventional 60 cycle, 115 volt alternating cur- 'rent source with the rectified negative pulses appearing across resistor 26 having a peak negative swing of from 50 to volts. 'The resistor 26 may be. approximately 3,000 ohms, the resistor 22 one megohm, the power source '20 may be 200volts D. C. and the bias source'40 may be "l0 volts D. C! for the electrode material and gaseous pressure'indicated previously. The negative signal pulse applied to the lead 36 may be approximately 5 volts magnitude. It is to be understood that these parameters may be varied withiriawide range and should not 'beconsidcred limiting as to the scope of the invention as the details of a preferred embodiment are described only for purposes of illustration and explanation.

A glow discharge is initially established between the anode 12 and the cathode 14 by the voltage of source 20 which is above the breakdown voltage of the gas. This discharge is shielded from view by the cylindrical structure 17 so as to produce no appreciable visible light. A negative signal pulse applied to the lead 36 and cathode 16 initiates a discharge on cathode '16 where the glow is visible and since the first discharge has ionized the gas, the voltage required to induce the second discharge is small. The rectified 60 cycle negative pulses appearing across the resistor 26 extinguish the glow to the upper cathode 16 but the glow is reestablished if the applied signal pulse is still on. This occurs due to the fact that v the voltage drop across the cathode 114 and anode 12 may not change and the negative pulses from the 60 cycle source cause the anode potential to be lowered to such a degree that a glow may not be sustained at this time between anode 12 and cathode 16.

Each signal pulse applied lowers the voltage of the cathode 16 and a greater voltage difierential exists between this cathode and the anode so that a discharge strikes therebetween in the absence of pulses from the 60 cycle source. However, each subsequent 60 cycle pulse, extinguishes this glow. As a result, with a continuous series of 5 volt signal pulses applied or with a continuous voltage level of this magnitude applied, the visible glow discharge to cathode 16 is turned on and elf repeatedly. Since this occurs at a 60 cycle rate there is no visible flicker but once this voltage level or series of signal pulses is stopped, there is a complete absence of visible glow indicating this oc- In the embodiment that has been described the cathodes 14 and 16 have had a particular structure conducive to their visual function, however, the particular configuration may be varied without departing irom the spirit of the invention. It is contemplated that a portion of the envelope It may be opaque 'to obscure the glow to cathode 14, for example, or the entire envelope may be opaque with'the exception of a small region adjacent the cathode 16. With such structural arrangements the physical shape of the cathodes themselves obviously need not be as shown 1. An indicator tube comprising a sealed envelope containing a gaseous atmosphere at glow discharge pressure and having an anode and a pair of cathode electrodes mounted therein, said anode and one of said cathodes comprising elongated rod-like elements axially parallel and spaced from one another, a cylindrical shield afiixed to said anode element and positioned in spaced relationship encircling said one cathode, said other cathode comprising a U-shaped element adjacent said shield and said anode, whereupon only a glow discharge to said other .cathode is visible external to said tube.

2. An indicator tube comprising a sealed envelope containing neon at a pressure of 20 millimeters of mercury and having an anode and pair of cathodes mounted therein, said anode and one of said cathodes comprising elongated rod-like elements arranged axially parallel and spaced from one another, a cylindrical element afiixed to said anode and arranged about said one cathode in spaced relationship, said other cathode comprising a U-shaped A element positioned adjacent said first cathode whereupon only a discharge to said other cathode is visible external to said tube.

3. An indicator tube circuit comprising a discharge device having a sealed envelope containing a gaseous atmosphere at glow discharge pressure with an anode and a pair of cathode electrodes mounted therein, said cathodes being arranged adjacent one another and said anode so that a glow discharge between a first one of said cathodes and said anode may lower the breakdown voltage between the second one of said cathodes and said anode with only the discharge to said second cathode being visible externally, a direct current voltage source coupled between said anode and said first cathode and adapted to establish a glow discharge therebetween, a source of signal pulses coupled to said second electrode and operable to establish a glow discharge to said second cathode, and means for periodically extinguishing said latter glow discharge so that a visible indication is attained only when a series of signal pulses is applied.

4. An indicator tube circuit comprising a discharge device having a sealed envelope containing a gaseous at- 'mosphere at glow discharge pressure with an anode and a pair of cathode electrodes mounted therein, said cathodes being arranged adjacent one another and said anode so that a glow discharge between :a first one of said cathodes may ionize the gas in the region between the anode and the second one of said cathodes, shield means within said envelope and operable to conceal a glow discharge to said first cathode, a direct current voltage source coupled between said anode and said first cathode and adapted to establish a glow discharge therebetween, a source of signal pulses coupled to said second electrode and operable to establish a glow discharge to said second cathode, and means for periodically extinguishing said latter glow discharge so that a visible indication is attained only when a series of signal pulses is applied.

References Cited in the file of this patent V UNITED STATES PATENTS 1,787,689 Lederer Jan. 6, 1931 1,863,702 Smith June 21, '1932 2,294,910 Johnson Sept. 8, 1942 2,309,525 Mohr Jan. 26, 1943 2,445,782 Kruithof et 'al July 27, 1948 2,612,617 Hagen Sept. 30, 1952 

